FIG. 1A is an example diagram illustrating a drive circuit according to conventional techniques. As shown, driver circuitry 100 receives control signal 105 to control a state of switch 135. Graph 170-1 in FIG. 1B illustrates a state of the control signal 105 as inputted to control drive circuit 100.
Prior to time T1, as shown in graph 170-1 of FIG. 1B, the control signal 105 is a logic zero (such as approximately zero volts). When the control signal 105 is a logic zero, switch 110-2 is set in an ON state and switch 110-1 is set to an OFF state, resulting in the output 125 driving the corresponding gate of switch 135 to −0.5 V. Note that the output 125 is −0.5 V (instead of ground) due to the voltage present across capacitor 120. In such an instance, switch 135 is open (OFF).
At time T1, the control signal 105 switches from logic low to logic high. This causes switch 110-2 to turn OFF and switch 110-1 to turn ON. In such an instance, the output 125 is 4.5 V (instead of 5 V) due to the −0.5 V across capacitor 120.
At time T2, the control signal 105 switches from logic high to logic low. This causes switch 110-2 to turn ON and switch 110-1 to turn OFF. In such an instance, the output 125 is set −0.5 V (instead of 0.0V) again due to the 0.5 V across capacitor 120.
One purpose of the capacitor 120 is to adjust a range of voltages that are produced at output 125. For example, instead of producing an output of 0 volts (for low voltage level drive) and 5 volts (and high voltage level drive), the output 125 of driver circuitry 100 outputs −0.5 V as a low drive output and 4.5 V as a high drive output.
Application of the −0.5 V for the low drive output level (such as before time T1 and after time T2) helps to ensure that switch 135 stays in an OFF state since the inherent capacitance Cm of switch 135 can cause a voltage spike on 125 (GATEL) thereby momentarily turning on switch 135 resulting in shoot through of current from node SW to the ground when the voltage of node SW changes rapidly from zero volts to 12 volts. In other words, the voltage coupling from node SW to the output 125 may be so high that the switch 135 momentarily turns to an ON state when it is supposed to be shut OFF.